It is tested that the effects of Alginate Synergist on the conversion characteristics of urea in soil and the loss ofammonia volatilization，which provides scientific basis for further development and utilization of alginate resources andthe improvement of the nitrogen fertilizer utilization rate.Indoor incubation method was adopted using fluvo -aquic soil and yellow-cinnamon soil as testedsoil，alginic acid -enhanced urea as testedfertilizer.Three treatments were setup: no fertilizerapplication(CK)，common urea(U)and alginic acid -enhanced urea(AU).Soil samples were collected periodically duringthe incubation period to test the contents of soil amidenitrogen，ammoniumnitrogen，nitrate nitrogen and the volatilizationvolume of ammonia.The results showed that1)Alginate Synergist effectively delayed the process of urea hydrolysis.2)Compared with common urea treatment(U)，the total amount of ammonia volatilization from AU treatment decreased by 3.74% to16.10%，and the ammonia volatilization rate decreased by 11.54%～ 21.57% and 18.18%～ 81.81% in fluvo-aquic soil and yellow-cinnamon soil，respectively.3)The peak value of ammonium nitrogen in the fluvo -aquic soil and yellow-cinnamon soil appeared on the 5 and 7d，respectively，and the content increased by 4.86%～12.02%.4)AlginateSynergist inhibited the conversion of ammonium nitrogen to nitrate nitrogen in soil from 5 to 7d.Inconclusion，AlginateSynergist can slow down the process of the hydrolysis ofurea，decrease the rate and loss amount of ammonia volatilization，and inhibit the conversion of ammonium nitrogen to nitrate nitrogen in the early stage ofincubation.Alginate Synergist has differenteffects on nitrogen transformation in differentsoils，with more efficient effect in yellow -cinnamonsoil.